Keywords

Introduction

Postharvest decay of fruits and vegetables is often a direct result of poor handling practices in the packinghouse environment. The wash water used in dump tanks for processing is among the various sources of pathogen contamination; thus, its proper sanitation is extremely important for delivering healthy products to the consumer and minimizing postharvest losses. Indeed, sanitation after harvest can reduce spoilage by 50% or more (Sargent et al. 2000). The most popular disinfecting agent is chlorine (hypochlorite) applied as spray or dip, but several alternative sanitizers of minor use during washing or storage of fresh produce are available, such as chlorine dioxide, ozone, ethanol, hydrogen peroxide, organic acids, and electrolyzed water (EW). This latter has gained importance in the food industry, representing a relevant technical advancement (Buck et al. 2002; Hricova et al. 2008; Feliziani et al. 2016; Rahman et al. 2016). It was firstly developed in Russia for water decontamination and regeneration (Kunina 1967), then it gained great interest for sterilization of utensils, meats, cutting boards, and, more recently, in livestock management and for the sanitation of the washing waters of fresh and minimally processed fruit and vegetables (Lee et al. 2004; Guentzel et al. 2010; Fallanaj et al. 2013; Gómez-López et al. 2013). This chapter will address EW generation, factors affecting its effectiveness, mechanism of action on microbes and hosts, and advantage and disadvantage on its use.

Generation of EW

In chemistry, the electrolysis is the process by which electrical energy is transformed into chemical energy, where an electric current passes through an electrolyte with subsequent migration of positive and negatively charged ions towards the negative and positive electrodes, respectively. EW is typically produced by electrolysis of dilute solutions of sodium chloride (NaCl) in an electrolysis cell with or without a diaphragm, which separates the anode (+) and cathode (−). Salts such as potassium chloride (KCl), magnesium chloride (MgCl2), sodium sulfite (Na2SO3), sodium hydrogen carbonate (NaHCO3) and many others (Table 12.1) can also be used (Buck et al. 2002; Fallanaj et al. 2013; Feliziani et al. 2016; Youssef and Hussien 2020). However, since a certain amount of chloride is contained in tap water, it would be possible to reactivate its free chlorine by electrolysis, although obtained amount is usually too low to be effective against pathogenic microorganisms (Nakajima et al. 2004). Recently a PE-1 water ionizer machine (Shenzhen, Guangdong, China) that use only naturally present salts in tap water allowed to obtain good results by selecting different levels of electrolyzing potentials (Hussien et al. 2017).

Table 12.1 Salts utilized as electrolytes to produce EW
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In an electrolysis cell divided by a membrane, two types of EW are produced: the acidic electrolyzed water (AEW) and the basic electrolyzed water (BEW), as displayed in Fig. 12.1. During electrolysis, the dissociated Cl− together with OH− move to the anode donating electrons to generate oxygen (O2), chlorine gas (Cl2), hypochlorite ions (ClO−), and hydrochloric acid (HCl), whereas positively charged ions, such as H+ and Na+, move to the cathode to accept electrons to generate hydrogen gas (H2) and sodium hydroxide (NaOH) (Siddiqui 2018). When the electrolysis cell is separated by a septum, species produced on the anode stream result in an acidic solution of pH 2–3, an oxidation-reduction potential (ORP) higher than 1100 mV, and an active chlorine content (ACC) of 10–90 ppm. Species produced on the cathode stream result in a basic solution of pH 10–13 and an ORP of −800 to −900 mV. When the electrolysis cell is not separated by a septum, neutral electrolyzed water (NEW), with a ORP of 750–900 mV and pH of about 7 is produced, because hydroxide ions (OH−) formed at the anode neutralizes the protons (H+) produced at the cathode (Deza et al. 2007). Compared to other types of EW, NEW has a longer shelf-life under certain circumstances (Rahman et al. 2010a, b).

Fig. 12.1
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Schematic representation of AEW and BEW generation using NaCl solution. (Hricova et al. 2008)

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Indeed, EW is usually prepared on site just before use, but Len et al. (2002) demonstrated that AEW stored in a closed and dark environment remains stable. In particular, AEW rapidly decreased ORP releasing Cl2 through the evolution of chlorine gas, thus rapidly reducing the biocidal effectiveness of the solutions. Len et al. (2002) observed a 100% loss of active chlorine and a 10% loss of ORP within a 4-day period for AEW stored in an open dark container at 25 °C. In contrast, loss of chlorine oxidants and ORP of NEW was substantially lower, with only 5% decrease of active chlorine and no significant loss of ORP after 4 days in a closed dark container at 25 °C (Guentzel et al. 2010). Another way to preserve the effectiveness of EW is to convert it into ice cubes for later use (Koseki et al. 2002). Finally, slightly acidic electrolyzed water (SAEW) with a pH of 5.0–6.5 (Fig. 12.2) and an ORP of 800–900 mV is produced by electrolysis of diluted solution of HCl alone or in combination with NaCl in an EW generation equipment using an electrolysis chamber without the membrane (Forghani et al. 2015). SAEW usually has high ACC (up to 200 ppm) and for this reason can be used in a diluted form; its main free chlorine is HOCl (Fig. 12.3). The bactericidal activity of hypochlorous acid was 80 times greater than that of hypochlorite ion (ClO−) for inactivating Escherichia coli at the same chlorine concentration and treatment time (Anonymous 1997). Therefore, SAEW may improve the bactericidal activity through maximizing the use of hypochlorous acid, thus reducing corrosion of surfaces and minimizing human health and safety issues side effects from off-gassing of Cl2 (Guentzel et al. 2008).

Fig. 12.2
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Schematic representation of SAEW generation using diluted solution of HCl. (From Xuan and Ling 2019)

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Fig. 12.3
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Chlorine profile change with pH. The activities of Cl2, HOCl, and OCl− produced during the electrolysis process are pH dependent, being Cl2 present at low pH, HOCl active at pH around 4.0–5.0, and OCl− effective at high pH. (From Al-Haq et al. 2005)

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EW is generally considered safer and less expensive than most traditional preservation methods. Various machines are manufactured around the world. The most common equipment used in published reports are ROX-20TA-U and ROX-10 WBE (Hoshizaki Electric Inc., Toyoake, Aichi, Japan), Remotex (Remote Co., Toshima-ku, Tokyo), model IKS 1005 (Mitsubishi Electric Engineering Co., Japan) (Al-Haq and Gómez-López 2012), and HRW-1500 (HuoRen-Jing-Chuang Medical Equipment Co., Ltd., Beijing) (Chen et al. 2020). In Europe the most common equipment in published reports producing NEW are manufactured by Adamant Technology (SA, Switzerland) (López-Gálvez et al. 2012; Fallanaj et al. 2013, 2016, 2015), Denora Next (Milan, Italy), Best Life (China), ATS unique technologies BV (The Netherlands), ATS (Holambra, SP, Brasil) and more recently by Aqanat Limited (Coxwold, York, UK).

Factors Influencing the Effectiveness of EW

The electrode materials play an important role in the production of oxidant species in relation to the current, temperature, salt, and type of electrolysis (Martínez-Huitle and Brillas 2008). Traditionally, platinum is used as the anode in the EW generator. A descending order of electrode materials in terms of efficiency in producing active free chlorine was proposed by Rahman et al. (2016): Ti/IrO2 > Ti/RuO2 > Ti/Pt–IrO2 > BDD (Boron-Doped Diamond) > Pt.

The influence of water hardness on the basic properties of EW has been reported by a few researchers (Pangloli and Hung 2013; Forghani et al. 2015). The authors reported that water hardness from 0 to 50 mg/L CaCO3 increases the ACC and ORP levels of EW, while decreasing the pH; however, water hardness higher than 50 mg/L was observed to inhibit the inactivation of E. coli O157:H7 by EW. The mechanisms of how water hardness changes the bactericidal efficacy of EW still remains unclear and requires more investigations. Moreover, Forghani et al. (2015) highlighted that pre-heating water before EW generation allowed to increase the ACC and the biocide activity.

In a fresh produce processing plant, sanitizers generally are used in the presence of organic matter, such as produce debris, soils, and microorganisms present on fruit and vegetable surfaces, all of which reduce sanitizer efficacy. Oomori et al. (2000) reported that organic matter, including amino acids and proteins, potentially react with ACC and change it into the combined form. For instance, Li et al. (1996) observed that the reduction rate of Bacillus subtilis var. niger by EW exposure for 20 min decreased from 100 to 19.5% after adding 10% bovine serum albumin (BSA) to AEW. Indeed, organic matters might wrap target microorganisms and protect the outer structures of microbial cells from the attack of EW (Park et al. 2009; Virto et al. 2005).

In addition, the bactericidal effect of EW is thought to be better on smooth surfaces than on rough ones (Koseki et al. 2004; Park et al. 2009). For instance, Park et al. (2009) observed that the reduction of E. coli O157:H7, Salmonella typhimurium, and Listeria monocytogenes on the surface of a tomato by AEW exposure was higher than that on the surface of green onions. The authors explained that the smoother surface of tomatoes accelerated the activity of chlorine species in EW to better contact with microorganisms.

Effect on Plant Pathogens

The modes of action of electrochemical treatment of water are still not completely understood. Evidences suggest that a direct oxidation at the anode surface and indirect oxidation in the bulk solution by oxidants produced from the substances present in the water are responsible for the inactivation of microorganisms (Anglada et al. 2009). In Aspergillus flavus morphological changes occurred both in the conidia and mycelia, such as cell wall shrinkage, partial cracking, chipping, and holes (Fig. 12.4, Xiong et al. 2014). Chlorine compounds, pH, ORP, and their combination are considered the main factors involved in the antimicrobial activity (Al-Haq et al. 2005) and these are reported as the mode of action of many gaseous and aqueous oxidizing agents (Finnegan et al. 2010). However, since EW is active in a wide range of ORP and pH values and in some cases free chlorine is not generated, it is conceivable that its activity is related but not limited to these three factors. EW seems to induce higher sensitivity to active chlorine by sensitizing the outer membrane to the entry of HOCl (Park et al. 2004a). HOCl is considered the most active of the chlorine compounds (Mahmoud 2007) produced during electrolysis, penetrating cell membranes and producing hydroxyl radicals, which exert the antimicrobial activity through the oxidation of key metabolic compounds (Albrich et al. 1986; Barrette et al. 1989; Hurst et al. 1991; Hricova et al. 2008). HOCl can change bacterial respiration destroying the electron transport chains and affecting adenine nucleotide pool (Albrich et al. 1981). Chlorine is considered responsible of: (a) disruption of protein synthesis; (b) oxidative decarboxylation of amino acids to nitrites and aldehydes; (c) reactions with nucleic acids, purines, and pyrimidines; (d) unbalanced metabolism after the destruction of key enzymes; (e) induction of DNA lesions with the accompanying loss of DNA-transforming ability; (f) inhibition of oxygen uptake and oxidative phosphorylation, coupled with leakage of some macromolecules; (g) formation of toxic N-chlorine derivatives of cytosine; and (h) creation of chromosomal aberrations (Feliziani et al. 2016).

Fig. 12.4
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Scanning electron photomicrographs of Aspergillus flavus conidia and mycelia. (a), normal mycelium; (b), mycelia treated with AEW; (c), mycelium treated with NEW; (d), normal conidia; (e), conidia treated with AEW; (f), conidia treated with NEW. Arrows show morphological changes in the conidia and mycelia, including cell wall shrinkage, partial cracking, chipping, and holes. Scale bars = (a and c), 30 μm; (b), 50 μm; (d–f), 5 μm. (From Xiong et al. 2014)

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ORP is also involved in the mode of action of EW but its effect on the deactivation of microbes is controversial (McPherson 1993; Venkitanarayanan et al. 1999; Kim et al. 2000, 2001; Al-Haq et al. 2002; Liao et al. 2007). Aerobic bacteria grow mostly at ORP range + 200 to +800 mV, while anaerobic bacteria grow well at −700 to +200 mV (Jay 1996). The high ORP in the EW could cause the modification of metabolic fluxes and ATP production (Fig. 12.5), probably due to the change in the electron flow in cells (Huang et al. 2008).

Fig. 12.5
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Effect of electrolyzed water (ew), sodium bicarbonate (NaHCO3) and electrolyzed NaHCO3 (eNaHCO3) on mitochondrial membrane potential of Penicillium digitatum spores represented as red/green florescence ratio (a), and on ATP content (b). For each treatment representative images of stained spores under fluorescence microscopy are showed (c). Water was used as a control. (From Fallanaj et al. 2016)

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Some authors suggested that the bacterial inactivation is primarily related to ORP and not to residual chlorine (Kim et al. 2000; Al-Haq et al. 2005). The high ORP of the solution affected fungi disrupting the outer membrane and facilitating the transfer of HOCl across the cell membrane, interfering on respiratory pathways (Liao et al. 2007). For example, it could cause damage to E. coli O157:H7, and attacked inner and outer membranes, causing necrosis of cells (Liao et al. 2007), with damage verified by microscopy (Feliciano et al. 2012). In case of NEW, produced by using diamond electrode and NaHCO3 as electrolyte, the activity of free chlorine was negligible and the pH little above the neutral value (Fallanaj et al. 2013); as reported also by Jeong et al. (2009), Fallanaj et al. (2013, 2016) ascribed the observed inactivation of Penicillium spp. population to electrochemical production of non-chlorine-based oxidants, such as hydrogen peroxide (H2O2), peroxymonocarbonate (HCO4−), and reactive oxygen species (ROS). In addition, the thin film-coated diamond electrode is known to produce by itself active oxygen species in a higher amount as compared to other anodes and, in presence of carbonate/bicarbonate-containing solutions, it can produce peroxycarbonate and derivatives, acting as strong disinfectants (Furuta et al. 2004). In addition, a paper by Fallanaj et al. (2016) demonstrated that electrolyzed NaHCO3 solution, when applied in wounds nearby the ones inoculated with the pathogen, was able to control P. digitatum infections in citrus fruit and a significant up-regulation of defense-related genes coding the enzymes chitinase, peroxidase, and phenylalanine ammonia-lyase was observed in treated tissues. Differences in mycelia micromorphology of Penicillium species treated with various EW and untreated were displayed in Fig. 12.6 and Fig. 12.7 employing scanned electron microscopy (Youssef and Hussien 2020). Based on above results on the mode of action of EW, its antimicrobial effect derives from the combined action of pH, ORP, free chlorine, and other still unknown active substances (Huang et al. 2008); in addition, the induction of tissue resistance should be considered as another important aspect of the multiple mechanism of action of this technology (Fallanaj et al. 2016).

Fig. 12.6
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Scanning electron microscope images of Penicillium digitatum-mycelium with free and linearly shaped hyphae (controls a and e). P. digitatum-mycelium in the presence of BEW generated by sodium metabisulphite (b), potassium sorbate (c) or potassium carbonate (d). P. digitatum-mycelium in the presence of AEW generated by sodium metabisulphite (f), potassium sorbate (g) or potassium carbonate (h). (From Youssef and Hussien 2020)

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Fig. 12.7
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Scanning electron microscope images of Penicillium italicum-mycelium with free and linearly shaped hyphae (controls a and e). P. italicum-mycelium in the presence of BEW generated by sodium metabisulphite (b), potassium sorbate (c) or potassium carbonate (d). P. italicum-mycelium in the presence of AEW generated by sodium metabisulphite (f), potassium sorbate (g) or potassium carbonate (h). (From Youssef and Hussien 2020)

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The pH also has its role in limiting the microbial growth; therefore, scientists also include it as one of the factors. Each microorganism has its own optimal growth range of pH; a low pH tends to destroy cell wall compounds (e.g. polysaccharides) and increase the permeability, resulting in the death of cell (McPherson 1993). Nevertheless, a low pH might not be sufficient to kill microbes, especially spores. Li et al. (1996) reported that the reduction level of B. subtilis var. niger can reach 100% after a 10-min AEW treatment, whereas it was only 1.06% for an HCl solution with the same pH. Therefore, most likely, the differences in effectiveness at different pHs is due to the high or low abundance of HOCl. In particular, at high pHs, the concentration of HOCl decreased, reflecting its dissociation to H+ and OCl− (Johnson and Melbourne 1996; White 1998).

Based on above literature there is no a consensus about EW mode of action against microorganisms (Table 12.2), but a lot of theories exist. Likely, multiple mechanisms are responsible of EW biocidal activity and this is theoretically confirmed by the absence of pathogen resistance.

Table 12.2 Studies conducted on the effect of EW water on various microorganisms
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Effect on Microbial Toxins

A study conducted by Audenaert et al. (2012) demonstrated that EW has potential to control Fusarium spp. in wheat grains during transport and storage although sub-lethal concentrations can result in increased deoxynivalenol (DON) biosynthesis. According to Zhang et al. (2012), soaking contaminated peanuts in an EW solution, the content of aflatoxin B1 (AFB1) decreased of about 85%. Moreover, they reported better results with AEW, suggesting a stronger decontamination effect of HClO than ClO−. On the same line, Suzuki et al. (2002) reported a strong reduction of the mutagenesis effect of AFB1 against Salmonella typhimurium TA-98 and TA-100 strains after the exposure of the toxin to the AEW.

Effect on Plants

Considering a holistic approach to the crop protection, it should be taken into account the effect of EW not only against the pathogens, but also on the crop. It has been demonstrated that SAEW inhibited the growth of broccoli sprouts, but increased sulforaphane content (Li et al. 2018). Another study conducted on Chinese cabbage highlighted that foliar application of EW solution could enhance the photosynthetic rate, leaf number, and yield; instead, root applications could increase the content of vitamin C (Hou et al. 2011). The application of EW on harvested sugarcane during summer months showed relatively less decline in Commercial Cane Sugar (CCS), sucrose, and purity of juice compared to untreated and water-treated control (Solomon and Singh 2009).

The effect of EW water on respiration rate is variable; it can increase, decrease, or remain unchanged. After AEW treatment, it has been reported that the respiration rate increased in lettuce and cabbage (Koseki and Itoh 2002). In contrast, an EW treatment on leek, white cabbage, and mizuna baby leaf, reduced the respiration rate significantly (Vandekinderen et al. 2009a, b). Finally, a NEW treatment on grated carrots and iceberg lettuce did not influence the respiration rate (Vandekinderen et al. 2008; Vandekinderen et al. 2009c). Moreover, depending on the fruits or vegetables and especially for “minimally processed” produce, the treatment with EW could have some effects on the nutritional and phytochemical composition, due to the oxidation nature of the EW and/or by leaching of substances from vegetable tissue due to water-vegetable surface contact (Al-Haq and Gómez-López 2012). Other researchers showed that changes in respiration rate during cold storage of cabbages and broccoli could be avoided by EW (Gómez-López et al. 2007; Navarro-Rico et al. 2014).

Electrolyzed Water and Quality of Produce

It is well known that fruit and vegetable quality is becoming more relevant than market price to most of the consumers. Unfortunately, most of research accounts have tested the effect of treatment on pathogens, while any possible negative consequence on fruit quality is not often acknowledged. Few studies were performed to investigate the effect of EW on produce quality. Youssef and Hussien (2020) summarized that neither BEW nor AEW have any harmful effect in terms of citrus quality including weight loss, total soluble solids, citric acid, ascorbic acid, pH and color index. Some scientists found no statistical difference in color index of lettuce, broccoli, strawberry, and date palm before and after EW treatment (Park et al. 2001; Hung et al. 2010a, b; Jemni et al. 2014). Also, EW application proved to have no harmful effect on iceberg lettuce and white cabbage quality with regard to vitamin C loss (Vandekinderen et al. 2009a, b). In addition, the use of EW had no obvious effect on both titratable acidity and pH in the case of date fruit and strawberry (Hung et al. 2010a, b; Bessi et al. 2014).

Effect on Removing Pesticide Residues

To ensure a sustainable production of fruits, vegetables, and grains, the farmers use a variety of pesticides to protect the crops from insects, mites, fungi, bacteria, weeds, etc. However, when humans and animals consume foods with pesticide residues, they can cause cumulative poisoning effects. Several physical, chemical, and biological methods including adsorption, oxidation, catalytic degradation, membrane filtration, and biological treatment have been developed in order to remove/inactivate pesticide residues. The use of EW as potential tool to remove pesticide residues, has been evaluated during the last years (Hao et al. 2011b; Sung et al. 2011, 2012; Wuyun 2011; Hao and Li 2006; Luo et al. 2014; Liu et al. 2015; Hu et al. 2016; Han et al. 2017; Qi et al. 2018), as shown in Table 12.3.

Table 12.3 Studies conducted on the effect of EW water in removing pesticide residues from produce
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They showed that a higher ACC and a longer treatment time leaded to greater reductions of pesticide residues. Moreover, the effectiveness was dependent on the chemical proprieties of the pesticides. For example, organophosphorus pesticides (e.g. dimethoate, chlorpyrifos, etc.), containing P=S double bonds and P–S or P–O single bonds, are easily attacked by chlorin (Deborde and von Gunten 2008) and hence can be degraded by the available chlorine in EW (Qi et al. 2018). In addition, a nucleophilic reaction has been reported to occur under acidic or alkaline conditions with the break of the double bond because of AEW low pH and high ORP value, whereas BEW with its high pH has proved to have a good emulsifying property (Wang and Han 2019). In summary, the EW has an obvious effect on the removal of pesticide residues on food without a significant decrease in quality (Wang and Han 2019).

Advantages of EW

The on-site production of the EW, whatever the use, represents a great advantage because there are no chemicals to purchase or store, except for an inexpensive salt (NaCl or others), eliminating the need for purchasing, transporting, storing, preparing and using traditional chemicals. EW has minimal impact on the environment (Koseki et al. 2002); particularly, NEW and BEW are safe for the environment and the operators since little chlorine is released to the air. If non-chlorine salts (e.g. NaHCO3) are used as electrolytes, health concerns with regard to chlorine in the air and in water are avoided and, consequently, the formation of chlorinated organic compounds including chloramines (NH2Cl), dichloramines (NHCl2), and trichloromethanes (HCCl3). These are respiratory irritants suspected to be carcinogenic (Roberts and Reymond 1994; Fallanaj et al. 2013; Citizens Concerned About Chloramine 2019. EW reverts to normal water after use, and its effectiveness has been verified within a large pH range (Park et al. 2004b). Since EW has multiple mechanisms of action, it is quite unlikely that resistance in target microorganisms will develop (Al-Haq et al. 2005).

After the initial cost of the apparatus for electrolysis, operational expenses become minimal (Bonde et al. 1999) and the capital cost of the on-site apparatus can often be recovered in less than a few years.

Indeed, in USA the unit cost per kilogram of electronically generated chlorine is significantly cheaper than liquefied chlorine gas, sodium hypochlorite solution, dry calcium hypochlorite, and cyanurate-based (TCIA) tablets (Grech and Rijkenberg 1992). The raw materials, water and sodium chloride, are found virtually everywhere (Venczel et al. 1997). Its use reduces the hazards associated with handling, transportation, and storage of concentrated chlorine solution (Nakagawara et al. 1998). The biocidal capacity of EW as compared to traditional chemical solutions permits the use of low dose rates, reducing the risk for environmental impact and the solutions should be less corrosive than alternate products. Lastly, the use of EW on various food commodities did not negatively affect the organoleptic properties, color, scent, flavor, or texture (Al-Haq et al. 2005; Hricova et al. 2008; Huang et al. 2008).

Disadvantages of EW

Strongly acidic EW and free chlorine content may be corrosive to some metals and may induce synthetic resin degradation (Tanaka et al. 1999), and hazardous chlorinated by-products can be produced. Its effectiveness may be hindered by the presence of organic substances (Oomori et al. 2000); its antimicrobial potential could be loosed quickly, once the apparatus is switched-off (Kiura et al. 2002). Depending on the electrolyte used and the pH (e.g. in AEW), pungent chlorine gas is formed that can cause discomfort to operators (Al-Haq et al. 2005). Excessive chlorine can be potentially toxic for plant produce (Grech and Rijkenberg 1992). AEW can induce phytotoxicity; for example, white spots and slight necrosis were observed on flowers and leaf edges of some ornamental bedding plants following an AEW foliar spray (Buck et al. 2003). A drawback could be also the need to switch-on the apparatus one or few hours before utilization to allow the bulk of water to become rich in antimicrobial oxidizing species (Fallanaj et al. 2013).

Conclusion

Disinfection of fresh produce and storage facilities is generally an important requirement for postharvest decay management. The applicability of disinfectants to control postharvest fruit decay depends on many aspects, i.e. on the fresh produce, the orientation towards organic or conventional agriculture, the time of the produce storage, the characteristics of the postharvest facilities, the possibilities to integrate the disinfection operations with other technologies and the know-how of the staff. In general, EW is characterized by a low impact on the environment and the operators, leaving no toxic residues or eliminating them on the food matrix. Because EW have multiple mechanisms of action it is quite unlikely that resistance in target microorganisms could develop. In view of the potential benefits to extend the storage period of fruit provided by the disinfectant agents, further studies could optimize their integration into current practices of postharvest manipulation.